Add a test that overflow does not happen

Author: alexcrichton

libm/src/math/floorf.rs

@@ -37,3 +37,11 @@ pub fn floorf(x: f32) -> f32 {
     }
     return f32::from_bits(ui);
 }
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn no_overflow() {
+        assert_eq!(super::floorf(0.5), 0.0);
+    }
+}